INTRODUCTORY ESSAY. 101 



and, though fully representing the Flora of the Polar regions, 

 contains so many types that are foreign to them (as Gentiana, 

 Ephedra, Valerianece, Corydalis), and some which are even 

 rare in Siberia, that it must rather be considered as a conti- 

 nuation of the Alpine Flora of Europe than a representation 

 of that of the Arctic zone. It displays one remarkable fea- 

 ture throughout its whole extent, a comparative paucity of 

 Cryptogamic plants ; and it is especially poor in those luxuriant 

 mosses of tall growth and succulent habit, which form vivid and 

 broad green tufts, loaded with rich brown capsules, and which 

 abound both in the Alps and Polar regions. This is no doubt 

 indirectly due to the elevation of the region, and directly to 

 the sudden accessions of great heat and drought, which are 

 the effects of a highly rarefied atmosphere, and which, though 

 strongly enough marked to check the development of Mosses 

 and Hepaticse, are not of sufficient duration to affect phseno- 

 gamic vegetation in the same degree. 



b. On the Distribution of Indian Plants as influenced by 

 Geographical Position. 



Hitherto we have solely considered the spread of plants in 

 India as influenced by climate, but geographical position is ac- 

 companied by such remarkable phenomena in vegetation, as 

 to indicate other influences, which demand some notice here. 

 The Floras of the frontier provinces of India, as we have re- 

 peatedly remarked, are identical with those of the countries 

 that surround them, and are continuous with them, and that 

 this should be so stands to reason ; but we sometimes see 

 a decided affinity between the Floras of areas separated by 

 oceans, deserts, or mountain-chains, between which it is un- 

 warrantable to assume that a migration of the species com- 

 mon to both, has taken place since the interposition of the 

 barriers in question, and which further present many natural 

 characters in common, which neither migration (if conceded 

 to any amount) nor climate will account for. We have already 



